I saw Suicide Squad twice, and it honestly underperformed my expectations. I'm really easy on movies, so I wouldn't categorize it as BAD, per se. At no point did it lose my interest, but it just wasn't good. It was well acted, the effects were appealing to me (avid movie watcher with no credentials), and the camera angles/cuts caught your attention, but the story was very slipshod. There was zero character development from anyone, half of the characters had no background info, and for some characters the audience was given no information at all.
My mom, who saw it with me the first time and loves going to the movies, said it reminded her of a Michael Bay film. It was eye candy, but the story was non-existent. The audience didn't have enough character info to CARE at all.
I read a story on Reddit that talked about some of the cuts from the DC higher-ups, and I think they really screwed the pooch on it. Things such as spoliers beginning background on Killer Croc, with his upbringing and how he thought he was "beautiful in his own way," in a similar way to Drax in Guardians of the Galaxy; Diablo with his sob story; Harley Quinn, specifically the psychological battering she took in her love/hate relationship with the Joker and a moment of growth where she spurns him for the Squad; Captain Boomerang, with more background, emotional investment from the audience, and comical relief; The Dr. Moon/Flag relationship with dates, dialogue, and a different opening of the movie that shows Dr. moon wandering through the jungle and discovering the witch; and that just names a few. I think DC really screwed the pooch here by trying to focus too much of the intro/story arc on Will Smith and his daughter. Ironically enough, I think DC tried too hard to copy the Marvel model (specifically GotG) because of the "depressing" reviews that BvS got and ended up straying too far away from what the movie was about- a dark, alluring squad of bad guys that are still bad guys in the end but who somehow keep your eyes glued to the screen. By trying to frame them as good while limiting their characters to caricatures of bad, and then throwing them back in jail to end the movie, the movie was just too inconsistent to be great, which I think it really could have.